The best possible news...
A shattered piston ring is the proximal cause of my engine failure. When I started to tear down my ailing engine and think about causes, the very best possible outcome seemed to be a broken ring. Given that all the components in the head measured within spec, and the cylinder wall seems unblemished, I was beginning to wonder if i would take the piston out and find it undamaged. That would have left only the cooling system and the dreaded governor as possible culprits. The thermostat came out of the head with some difficulty, and it was sufficiently encrusted to make me suspicious that a clogged thermostat and clogged hoses were part of my problem (the hoses were pretty crusty when I got them off). Surprisingly, it still worked when put in a pan of water, but that doesn't mean it was entirely functional in the running engine. Inspection of the cooling ports in both the block and the head suggests that the rest of the system is unoccluded, but a blockage at t...